Hi Dave,
regarding your isolation transformer and its electrostatic shielding you claim that this "basically cuts its capacitance completely down to zero". Well I challenge you on that one.
My experience is: "Nothing isolated has a capacitance of zero". Parasitic capacitance is every where :-)
I have a very similar isolation transformer (HP M1389A), which also has this kind of shielding (protective earth wire going into the toroidal transformer).
When i run it at 230V, the output voltages of the secondary contact measured with the 10M? DMM show 160V (at one side, 67V on the other). As far as i know, the VDE 0701/0702 (similar to PAT, portable appliance testing) specifies a 2k? resistor to ground for testing touch currents on the isolated parts of a device. These 2k? represent the internal resistance of the human body. The current limit is specified at 0.5mA.
The 160V @ 10M? drop down to about 200mV when grounded with 2,2k?.
0.2V/2200? = 91µA
230V / 91µA gives about 2.5M? impedance (@50Hz).
With X
c = 1/(2*pi*50*C) I get an effective capacitance of about 1.27nF or 1270pF.
Close, but not quite zero ;-)
Measuring capacitance between secondary and ground also gives me a value of 1,15nF (all measurements done with a Brymen BM257)
BTW, have you seen
this thread (replies #4ff) about isolation transformers? I was shocked to see that there seem to be pseudo isolation transformers, which have a direct ground connection on the secondary side of the transformer. Such devices should not be called
isolation transformers.